The use of diagnostic ultrasound in obstetric practice has increased rapidly in the last decade. A number of adverse biological effects of diagnostic ultrasound have been described in vitro and animal studies. Research on humans has not documented adverse effects, but has been limited by inadequate sample sizes and follow-up. The necessary studies to assure safety have not been done. The proposed study will use a very large data base containing Medicaid billing data to describe ultrasound use for almost 300,000 pregnant women. From these, a healthy short of exposed and nonexposed pregnant women who have had uncomplicated pregnancies will be identified, excluding all pregnant women who have had reported conditions that might increase the risk of an adverse pregnancy outcome and be associated with ultrasound use. Four controls will be randomly selected per study subject, matched by five year age strata. After linking maternal records to the records of their offspring, the exposed study subjects will be compared to the controls for age; race; county of residence diseases, both before and during pregnancy; number of routine antenatal visits; medications dispensed during pregnancy; and pregnancy outcomes, including illnesses in offspring, congenital anomalies, hospitalizations, and deaths during the first year of For those with full term pregnancies, we will stratify by trimester of exposure and repeat the above analyses. If specific adverse outcomes appear to be associated with ultrasound use, they will be further examined according to the timing and frequency exposure and associated diseases and drugs. Statistical analyses will include calculating relative risks and 95% confidence limits and logistic regression, if indicated, to control for the joint effects of multiple confounders. Varying follow-up time will be accounted for using Kaplan-Meier Survival curves and Cox's regression, if indicated. Given the very large number of pregnant women included in this study, if no increased risks are detected for those exposed to ultrasound, we believe we can be assured about the safety of ultrasound use in uncomplicated pregnancies. If increased risks are detected, we will be able to analyze the association in detail by subgroups according to timing and frequency of exposure. This research involving the disciplines of obstetrics and gynecology, pediatrics, and clinical epidemiology, would represent a major step towards answering the question about the safety of ultrasound use in pregnancy.